CMOS rectangular-array photosensor arrays are commonly used as image sensors in cameras. These arrays have an array of N by M (when N and M are both greater than 1 and often are unequal) photodiode-based photosensors each having at least one selection transistor having a gate coupled to a selection line. These arrays typically have precharge transistors arranged so to apply charge to the photodiode, and one or more sense transistors arranged to read post-exposure charge from the photodiode onto one or more bit lines; these arrays typically also have decoder-drivers configured to drive the selection lines and gain amplifiers fed by the bit lines, and in some embodiments may incorporate other circuitry.
Traditionally, photodiodes of photosensor arrays are read onto a bit line, sometimes through a unity-gain source-follower. The bit line is in turn multiplexed onto a gain amplifier. Gain amplifiers typically have gain controlled by a ratio of two resistors or two capacitors that provide feedback around the amplifier.